First of all, which heli are you having trouble with?
Second, what makes you think you have a static discharge problem as most belt-driven helis do not suffer from this problem.
The one most notable exception is the Align Trex 500. The inside diameter of the tail boom, along with the diameter of the front and rear pulleys, allows the belt to rub on the inside of the tail tube where the belt exits at both ends. This rubbing is a prime source of static electricity. Most other belt-driven helis have sufficient clearance between the belt and the tail tube such that the belt does NOT rub on the tube.
You may not be seeing static discharge problems as much as problems with your power system and its ability to supply sufficient power to the radio at all times.
All materials in the real world are made up of atoms -- the smallest unit of the material that exists that still IS the material. For instance, a gold nugget is a gold nugget. Take the nugget and start breaking it into smaller and smaller pieces. All of the small pieces are still gold. At some point, as you break the material down into smaller and smaller pieces, you get to the point where you are at the sub-microscopic level and are looking at individual atoms of gold. If you continue to break down the atom you no longer have gold, you have a nucleus, protons, electrons, and neutrons. Those particles by themselves no longer can be recognized as gold.
Protons are positively charged particles, neutrons have no charge, and electrons are negatively charged particles.
Protons and neutrons are generally bonded to the nucleus of the atom with strong bonds. The electrons on the other hand are more loosely bonded to the atom and can move from atom to atom readily Electrons orbit the nucleus with its tightly held protons and neutrons, and on the atomic scale, the diameter of the orbits are relatively large.
In materials that are electrical insulators, the electrons cannot move freely within the material and the electrons are tightly held to the nucleus. In an electrically conductive material, electrons can move freely and the electrons are loosely held.
Electrons can be moved between materials easily. If you bring two different insulating materials together, electrons may be transferred from one of the materials to the other. When you then separate the two materials, one may have an excess of electrons (it becomes negatively charged, the other may have a shortage of electrons, it becomes positively charged. Since the items are insulators, the excess charge remains, the items become "charged" and have "static electricity". Bring either one into contact with a conductor, the excess charge is bled off rapidly, producing in many cases, a spark.
You can generate a static charge by bringing two materials together, by separation, or by friction. If you have a tape dispenser and a three hole paper punch full of the leftover holes, try the following experiment:
Distribute some of the punched holes on a table top. Pull a length of tape off the dispenser, then hold it over the loose paper dots. The paper dots will jump up to the tape long before the tape touches them. The action of simply pulling the tape off its roll created a static charge on the tape. As the charge of the paper dots and the tape is different, the difference in static charge causes the tape to attract the dots. Note that the tape and the dots are both insulators.
If you have a balloon handy, blow it up and tie it off so you have a nice, full balloon. Rub the balloon on your hair (if you aren't bald) a bunch of times, then stick the balloon to the wall and let go. The act of rubbing the balloon on your hair created a static charge on the balloon. This excess charge allows the balloon to stay stuck to the wall. The wall and the balloon are both insulators.
We all know what happens in the winter after walking across a carpeted floor, then touching a doorknob or your favorite electrical gear -- you get zapped and see a spark. Walking across the carpet builds up a static charge on your body, when you touch the conductive doorknob or other item, that excess charge is rapidly bled off, resulting in a spark and the zapped feeling.
Static electricity, then, is the build up of electrical charge upon an object, and the charge is there waiting to be bled off.
In the case of the belt-driven heli, the belt itself is made of rubber or other insulating rubber-like material. The pulleys at the ends of the belt, typically made of plastic, are also insulators. If they are metal, they may still be isolated electrically from the heli frame by plastic, non-conductive mounts.
As the rubber belt turns the pulleys, you are repeatedly bringing two different insulative materials together, and separating them. As the pulley/belt/boom are electrically isolated, a large amount of static electricity can build up. At some point, the charge builds up to the level where it finally ionizes the air around it, creating a momentary conductive path in the air, and ending up on a conductive surface close-by. Maybe part of the tail case, maybe a bolt in the tail boom or front-end of the tail assembly.
The belt-driven tail can be likened to that of a Van de Graaf generator --http://en.wikipedia.org/wiki/Van_de_Graaff_generator
The spark may be several thousand volts, at very small current, but it creates a lot of broadband RF noise. With tail boom mounted gyros (keeping in mind that gyro case materials are usually conductive to reduce the effect of stray electrical fields upon the sensing element and signal processing), it was believed (and later actually captured on film) that the spark jumped between the tail boom and the gyro case. This sudden discharge would reset the gyro, causing bad things to happen in the air. The static discharge could conceivably upset the digital logic in a gyro or 2.4 GHz receiver. Not because it's an RF problem, but because digital logic is easily upset by electrical glitches.
Several methods have been successfully implemented to counter the effects of static discharge.
1. Ground the tail pulley/tail case to the frame. Many belt driven helis have (or had) an idler roller on the tail case that was in contact with the belt and kept it from slipping on the pulley. A small wire was attached to this bolt, and then attached to the tail boom (conductive if made of aluminum, steel, or even carbon fiber). The front end of the boom also had a small wire connecting the front of the boom to one of the frame bolts. As long as the frames are aluminum or carbon fiber, they are conductive. That same point in many installations would also be tied directly to the main battery negative terminal. This setup prevents the buildup of electrical charge in the tail boom, eliminating the nasty spark and its detrimental effects.
2. Periodically spray the drive belt with a static dissipative material (silicone spray, fabric softener, anti-static spray..).
3. Coat the tail drive belt with graphite powder (sold as a dry lock lubricant) or rub the belt down periodically with a soft-lead pencil (there is graphite in the pencil lead), making the belt conductive enough to prevent static build up.
4. Replace the belt-drive with a torque-tube setup.
5. Static electricity buildup is more prevalent when the humidity is low, as moisture in the air is conductive and has a static dissipative effect.
so how does the static get to the boom if there is no conductive contact from the belt to the boom??
The same way lightning goes from cloud to ground. Or from your finger to the doorknob. If you get a large enough static potential voltage difference, the excess charge will create an ionized path through the air to the closest point with an opposite charge.
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